Semiconductor device geometries have dramatically decreased in size since their introduction several decades ago. Modern semiconductor fabrication equipment routinely produces devices with 250 nm, 180 nm, and 65 nm feature sizes, and new equipment is being developed and implemented to make devices with even smaller geometries. The smaller sizes, however, mean device elements have to work closer together which can increase the chances of electrical interference, including cross-talk and parasitic capacitance.
To reduce the degree of electrical interference, dielectric insulating materials are used to fill the gaps, trenches, and other spaces between the device elements, metal lines, and other device features. The dielectric materials are chosen for their ease of formation in the spaces between device features, and their low dielectric constants (i.e., “k-values”). Dielectrics with lower k-values are better at minimizing cross-talk and RC time delays, as well as reducing the overall power consumption of the device. Conventional dielectric materials include silicon oxide, which has an average k-value between 4.0 and 4.2 when deposited with conventional CVD techniques.
While the k-value of conventional CVD silicon oxide is acceptable for many device structures, the ever decreasing sizes and increasing densities of device elements have kept semiconductor manufacturers looking for dielectric materials with lower k-values. One approach has been to dope the silicon oxide with fluorine to make a fluorine-doped silicon oxide film (i.e., “FSG” film) with a dielectric constant as low as about 3.4 to 3.6. Another has been the development of spin-on glass techniques that coat the substrate with highly flowable precursors like hydrogen silsesquioxane (HSQ) to form a porous low-k film.
More recently, silicon-oxygen-carbon (Si—O—C) films have been developed with k-values of 3.0 or less. These low-k films are often deposited by the chemical vapor deposition of carbon-silicon and oxygen precursors on the substrate. While these Si—O—C films have lower k-values than pure and fluorine-doped silicon oxide films, they also tend to be substantially more porous, which can have negative consequences. Porous films are prone to increased absorption of water, which can increase the k-value of the film. Porous films also have higher “wet etch rate ratios” (WERRs) that can make the film more prone to corrosion and stress cracking. Thus, there is a need for new methods of depositing low-k carbon based films with reduced porosity, lower WERR values, and less cracking. These and other issues are addressed by embodiments of the invention.